1. Field of the Invention
The present invention relates, generally, to an improved process for the production of polysaccharides by fermentation of glucides in the presence of selected microorganisms and effective nitrogen-containing compounds; and, more especially to the fermentation of, e.g., sugars with a microorganism of the genus Xanthomonas in the presence of an inorganic nitrogen-containing compound which serves as the sole nitrogen source for the fermentation process.
2. Description of the Prior Art
Polysaccharide gels are known agents particularly adapted for, e.g., the assisted recovery of petroleum. Numerous and diverse processes are conventional for their preparation and include, inter alia, fermentation in the presence of certain microorganisms.
Conventionally, in the production of extracellular polysacchardies by fermentation of glucides with microorganisms, the medium to be fermented comprises a source of phosphorous, a source of magnesium which acts as an enzyme activator and a source of nitrogen. In the typical prior art processes to this end, the nitrogen is present as an organic compound which may consist of "distillers' solubles" (U.S. Pat. No. 3,000,790), of bran, whole cereal flours such as sorghum, soya, or maize (U.S. Pat. No. 3,271,267), or of "corn steep" (U.S. Pat. No. 3,355,447). However, these organic compounds, which provide the necessary assimilable nitrogen, suffer a significant disadvantage insofar as the same additionally introduce insoluble impurities which are, in turn, evident in the polysaccharide extracted from the fermented must.
Such unwanted impurities, in addition to imparting undesirable coloration and turbidity to the gel reconstituted from the extracted product, render that gel product unsuitable for certain uses such as, for example, the aforenoted assisted recovery of petroleum. Indeed, the presence of these impurities, which are of low solubility and consist of large protein molecules, reduces the filterability of the gels thereby obtained from the polysaccharides and, concomitantly, render it exceedingly more difficult for these gels to penetrate within the interstices of the rock formations. Consequently, in order to render these gels efficacious, it has become necessary to employ various subsequent techniques of purification, all of which are expensive and few of which are totally satisfactory in terms of yielding a usable product.
In an effort to overcome the problems attendant use of organic sources of nitrogen, various alternative techniques have been proposed. Most significant among these is the use of certain inorganic nitrogen compounds as a source of nitrogen for the production of polysaccharides by bacteriological conversion, especially by the Xanthomonas.
One such technique proposes the use of ammonium chloride as a source of nitrogen in these environments. See, M. P. Starr, "The nutrition of phytopathogenic bacteria-I. Minimal nutritive requirements of the genus Xanthomonas", J. Bacteriology, v. 51, pp. 131-143, 1946. However, while such compounds may be efficacious in the abstract, pragmatically they give rise to other problems more serious than that sought to be overcome, inasmuch as the presence of chloride ions in industrial apparatus causes severe corrosion of the equipment. This is significant not only in terms of the need to replace capital equipment, but by introducing the products of corrosion into the mixture.
Another alternative is proposed in the U.S. Pat. No. 3,391,060 to McNeely, which suggests the use of ammonium nitrate as a suitable source of nitrogen, its presence restricted to the final fermentation stage. Consequently, the process of McNeely requires the use of up to four prior process steps, which are conducted upon media principally containing soya peptone as the source of nitrogen. Also, in practicing the process of that patent, the concentration of ammonium nitrate in the final fermentation medium is critical to successful realization of the objects and advantages of the disclosed invention.
Therefore, the need exists to simply, economically, and yet efficiently provide a process for the production of polysaccharide gels, which gels exhibit the required high viscosity and yet, additionally, possess a high degree of filterability.